Degradable foamed shoe sole, materials and method for producing the same

Abstract

A material for manufacturing biodegradable foamed shoe soles, a biodegradable foamed shoe sole, and a method for manufacturing the same are disclosed. The material comprises: 70 wt% to 95 wt% of a first biodegradable material containing polybutylene adipate terephthalate (PBAT); and 5 wt% to 30 wt% of a second biodegradable material or 0.5 wt% to 4 wt% of a foaming accelerator, wherein the second biodegradable material contains polyvinyl alcohol (PVA), and the foaming accelerator contains lignin. The method comprises: a melting step, melting the material; a mixing step, uniformly mixing the molten material with a supercritical gas to obtain a polymer melt; an injection step, injecting the polymer melt into a mold; and a foaming molding step, depressurizing the mold and cooling the polymer melt to foam and shape it, thereby manufacturing a biodegradable foamed shoe sole.

Description

Technical Field

[0001] This invention relates to a biodegradable foamed shoe sole, its manufacturing materials and manufacturing method, and in particular to an environmentally friendly biodegradable foamed shoe sole, its manufacturing materials and manufacturing method. Prior Technology

[0002] Globally, approximately 23 billion pairs of footwear are produced annually. It is estimated that about 22 billion of these shoes end up in landfills after use, taking hundreds of years to decompose, thus placing a significant burden on the environment. The complex materials used in shoes make disassembly difficult, a major reason for the challenges in recycling. Therefore, developing biodegradable footwear materials has become a key strategy for solving the footwear waste problem.

[0003] Based on the functional requirements of cushioning, comfort, and elasticity, foam soles, as the most important functional component of shoes, are currently mainly made of plastic (mainly EVA, TPU, etc.) or rubber materials through foaming technology.

[0004] Chinese invention patent announcements CN101613486B and CN102229707B disclose a method for preparing polybutylene adipate terephthalate (PBAT) foam particles, a biodegradable material. In this method, PBAT is crosslinked with a chain extender and then subjected to supercritical gas foaming to obtain a foamed body.

[0005] Chinese invention patent application publication CN105802143A and collaborative patent publication PCT / CN2021 / 077197 also disclose a technique for producing foamed materials by supercritical CO2 gas foaming of PBAT modified materials crosslinked with chain extenders, and disclose that the foamed materials can be used as foamed shoe materials.

[0006] However, the aforementioned prior art has the following problems:

[0007] First, compared to EVA or TPU, which are commonly used in foamed shoe soles, pure PBAT foam has an excessively high compression set due to its physical properties, making it unsuitable for footwear materials. Therefore, PBAT polymers crosslinked with chain extenders must be used to obtain a better compression set (reduced to 50% to 60%).

[0008] Secondly, although chain extenders can improve the problem of insufficient strength and easy collapse of pure PBAT foam, the chain-extended PBAT has a lower biodegradability due to the increased molecular weight (increased degree of polymerization) and the formation of permanent chemical cross-linking structure. In addition, unbonded chemical chain extenders will remain after the reaction, all of which are detrimental to environmental sustainability.

[0009] Third, most supercritical fluid foaming processes currently used in the industry employ autoclave foaming processes, including autoclave bead foaming or autoclave sheet foaming. In these processes, the polymer must first be formed into beads or a primary preform using an injection molding machine, then placed in a pressure vessel. Supercritical gas is then injected, and the pressure is maintained for a period to allow the gas to permeate into the beads or preform. The pressure is then rapidly released to obtain the primary foam, which is subsequently placed in a mold for a second molding process. However, while supercritical gas autoclave foaming improves upon the shortcomings of traditional chemical foaming, this static foaming method requires secondary foaming (beads or preform) and secondary processing (molding sheets), resulting in low production efficiency due to the multiple steps involved.

[0010] Fourth, since most polymer melts have a high solubility for carbon dioxide (CO2), and CO2 diffuses quickly in the melt for autoclaving where gas diffusion is required for a long time, CO2 has been used as a supercritical blowing agent gas in previous technologies. However, foams made with CO2 as a supercritical blowing agent gas have the following disadvantages: (1) the gas is easy to escape, which makes the foam easy to deform and collapse; (2) in order to maintain the supercritical state of CO2, a large pressure needs to be applied, and a large cost and attention are required for the investment in pressure vessels and the maintenance of industrial safety; (3) CO2 is a greenhouse gas and is not environmentally friendly. Summary of the Invention

[0011] [The problem the invention aims to solve]

[0012] To address the problems of the prior art, the present invention aims to provide a biodegradable foamed shoe sole, its manufacturing material, and its manufacturing method, wherein the performance of the foamed shoe sole made by supercritical nitrogen (N2) injection molding using PBAT and other modified materials in terms of compression set is improved.

[0013] [Technical means to solve the problem]

[0014] To achieve the above objectives, according to an embodiment of the present invention, a material for manufacturing biodegradable foamed shoe soles is provided, comprising: 70 wt% to 95 wt% of a first biodegradable material; and 5 wt% to 30 wt% of a second biodegradable material and / or 0.5 wt% to 4 wt% of a foaming accelerator.

[0015] In one embodiment of the present invention, the first biodegradable material may comprise polybutylene terephthalate (PBAT).

[0016] In one embodiment of the present invention, the second biodegradable material may contain polyvinyl alcohol (PVA), and the foaming accelerator may contain lignin.

[0017] In this invention, both the second biodegradable material containing PVA and the foaming accelerator containing lignin have the ability to improve the compression set of pure PBAT foam. Therefore, in this invention, they can be added as another component besides the first biodegradable material to improve the compression set.

[0018] In particular, as a component complementing the properties of the first biodegradable material, the PVA in the second biodegradable material also exhibits excellent ductility, tensile strength, tear strength, and abrasion resistance. The physical properties of PVA depend on its degree of polymerization and basicity.

[0019] The degree of polymerization of PVA reflects its molecular weight. The higher the degree of polymerization, the higher the tensile strength, tear strength, and abrasion resistance of PVA.

[0020] Therefore, in one embodiment of the present invention, the molecular weight of PVA can be from 18,000 d to 130,000 d.

[0021] On the other hand, PVA is manufactured by alkaline hydrolysis of PVAc, which replaces the originally less polar acetyl group (Ac) with a more polar OH group. Since the hydroxyl group is more polar than the acetyl group, the degree of alkalinization of PVA reflects the polarity of PVA. The higher the degree of alkalinization, the greater the polarity and the better the compatibility with more polar molecules.

[0022] Therefore, the strength of PVA and its compatibility with other polymer molecules can be adjusted by changing the degree of polymerization and basicity of PVA.

[0023] In one embodiment of the present invention, the alkalinity of PVA can be between 70% and 99%.

[0024] In one embodiment of the present invention, the second biodegradable material may further contain 15 wt% to 35 wt% plasticizer based on the total weight of the second biodegradable material.

[0025] In one embodiment of the present invention, the plasticizer may include at least one of small molecule polyols, polyethylene glycol, glycerides, and citrates.

[0026] In one embodiment of the present invention, the first biodegradable material and the second biodegradable material may each be in the form of independent colloid particles.

[0027] In another embodiment of the present invention, the first biodegradable material and the second biodegradable material may be in the form of modified colloids.

[0028] To achieve the above objectives, according to one embodiment of the present invention, a method for manufacturing a biodegradable foamed shoe sole is also provided, comprising: The melting step involves melting any of the above-mentioned materials used to manufacture biodegradable foamed shoe soles; The mixing step involves uniformly mixing the molten material with a supercritical gas to obtain a polymer melt containing the supercritical gas. The injection step involves injecting the polymer melt into a mold; and The foaming molding step involves depressurizing the mold and cooling the polymer melt within it, causing the polymer melt to foam and solidify, thereby producing a biodegradable foamed shoe sole.

[0029] In one embodiment of the present invention, the melting step, the mixing step, and the injection step are performed using a foam injection molding equipment, and wherein, In this melting step, the material used to manufacture biodegradable foamed shoe soles is fed into the feed tube of the foam injection molding equipment, where it is melted and stirred by means of a screw and heating. In this mixing step, the supercritical gas is further injected into the feed tube, where it is stirred and mixed with the molten material by the shearing force of the screw; and In this injection step, the polymer melt is injected into the mold through the injection nozzle of the foam injection molding equipment.

[0030] In one embodiment of the present invention, N2 is used as a supercritical foaming agent gas for foaming.

[0031] To achieve the above-mentioned objectives of the present invention, according to one embodiment of the present invention, a biodegradable foamed shoe sole is also provided, which is manufactured by any of the above-described methods for manufacturing biodegradable foamed shoe soles.

[0032] In one embodiment of the present invention, the biodegradable foamed sole has a foaming ratio of 7 to 9 times, a resilience of 45% to 70%, a compression set of 50% to 70%, and a shrinkage of 0.1% to 0.5%.

[0033] [Comparison with the effectiveness of previous technologies]

[0034] In this invention, by excluding the use of chain extenders, the biodegradability of foamed shoe soles can be improved, thereby promoting environmental sustainability.

[0035] In this invention, PBAT and PVA are modified to form PBAT / PVA modified materials (which can be further mixed with lignin) and then foamed, or PBAT and lignin modified materials are foamed. The addition of PVA or lignin increases the strength of the foam, thereby effectively improving the defects of pure PBAT foam in terms of compression set and / or hardness without the use of chain extenders.

[0036] Therefore, compared to pure PBAT foam, the foamed shoe sole made of modified materials of the present invention can have excellent properties such as lower specific gravity, higher resilience, and lower compression set.

[0037] According to a preferred embodiment of the present invention, N2 is used as a supercritical foaming agent gas. In addition to being less expensive than CO2, it solves the problems of easy CO2 gas escape when using CO2 as a supercritical foaming agent gas in the prior art, the high cost of pressure vessels and industrial safety maintenance required to maintain the supercritical state of CO2 gas, and the problem of easy deformation and collapse of the foamed shoe soles. Furthermore, since N2 has a larger specific volume, it is beneficial to manufacture foamed shoe soles with a larger foaming ratio, lower specific gravity, and lighter weight, thereby making the product lighter.

[0038] According to one embodiment of the present invention, a foamed shoe sole is manufactured by supercritical foaming agent gas injection molding, wherein, in the mixing step, the shear force of the screw is used to fully stir and mix N2 with the melt to overcome the problem that N2 has lower solubility and diffusion rate in the melt compared to CO2.

[0039] According to one embodiment of the present invention, foamed shoe soles are manufactured by supercritical foaming agent gas injection molding, which can be foamed and molded in one step without the need for secondary mold pressing or secondary processing, thereby solving the problem of low production efficiency caused by complex processes in the prior art.

[0040] As described above, the effects of the present invention are not limited to those exemplified above, and include a variety of other effects in this specification. Simple Explanation of the Diagram

[0041] Figure 1 is a flowchart of a method for manufacturing a biodegradable foamed shoe sole according to the present invention. Figure 2 is an apparatus diagram of a foam injection molding equipment for manufacturing biodegradable foamed shoe soles according to an embodiment of the present invention. Figure 3 shows the foaming effect of different biodegradable materials according to Example 1 of the present invention. Figure 4 shows the foaming results of supercritical gas autoclaving foaming and supercritical gas injection molding foaming according to Embodiment 2 of the present invention. Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the exemplary embodiments disclosed herein and the accompanying drawings.

[0043] The same component symbols are usually used to indicate the same component in the instruction manual.

[0044] The features of the various embodiments of the present invention may be combined or integrated with each other in part or in whole, and may be linked and operated in various technical ways, and the embodiments may be implemented independently or in association with each other.

[0045] This invention can be modified in various ways and has various embodiments, the specific embodiments shown in the figures will be specifically described below. The description of the embodiments is not intended to limit the invention to the specific embodiments, but should be interpreted as covering all modifications, similarities, and alternatives within the spirit and technical scope of the invention.

[0046] Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without making progressive improvements are within the scope of protection of the present invention.

[0047] Furthermore, detailed descriptions of known related technologies may be omitted in the following description of the present invention to avoid unnecessarily obscuring the subject matter of the invention.

[0048] This invention uses a supercritical gas foaming process, which eliminates the need for chemical foaming agents, thus meeting environmental protection requirements, and also produces foamed bodies with uniform micropores.

[0049] However, the industry currently widely uses supercritical gas autoclave foaming processes. The general process involves first using an injection molding machine to obtain a primary preform from polymer material, then placing the preform in an autoclave, injecting supercritical gas, maintaining the pressure for a period of time to allow the gas to permeate into the melt, and then rapidly depressurizing to obtain the primary foam. Subsequently, the primary foam is placed in a mold for a second compression molding.

[0050] Because this static autoclaving foaming process requires secondary processing, the process is complex and results in low production efficiency.

[0051] Therefore, this invention employs a novel process combining injection molding and supercritical gas foaming technology. Supercritical gas is injected into the feed tube of the injection molding machine, and the screw torque rapidly and thoroughly mixes the supercritical gas with the polymer melt. The supercritical gas-saturated melt is then pressurized and injected into the mold. After depressurization and cooling, the molded foam is directly obtained. This supercritical gas injection foaming technology is not yet widely used, especially not applied to the foaming process of the biodegradable material PBAT. [Foaming Material]

[0052] In this invention, by modifying a first biodegradable material (PBAT) with a second biodegradable material (PVA) or a foaming accelerator (lignin) in different proportions, a better modification ratio is explored, thereby enabling the manufacture of foams with excellent performance.

[0053] In addition to chemical chain extenders, prior art also adds nucleating agents to foamed materials to enable gases to rapidly develop into bubbles, which helps to form foams with smaller pores and uniform distribution. However, the nucleating agents used in prior art are inorganic fillers, such as talc or calcium carbonate.

[0054] In this invention, by using lignin as a foaming accelerator to replace the inorganic nucleating agent of the prior art, it has been proven that the bubble formation time can be significantly shortened. Since lignin is a biodegradable biomass material, from an environmentally friendly point of view, it is more in line with the goal of environmental friendliness than the nucleating agents commonly used in the prior art.

[0055] Therefore, the present invention provides a material for manufacturing biodegradable foamed shoe soles, comprising: 70 wt% to 95 wt% of a first biodegradable material; and 5 wt% to 30 wt% of a second biodegradable material or 0.5 wt% to 4 wt% of a foaming accelerator.

[0056] In a preferred embodiment, the material used to manufacture the biodegradable foamed sole may include: 70 wt% to 95 wt% of a first biodegradable material; 5 wt% to 30 wt% of a second biodegradable material; and 0.5 wt% to 4 wt% of a foaming accelerator.

[0057] The first biodegradable material may contain polybutylene adipate (PBAT). The second biodegradable material may contain polyvinyl alcohol (PVA). The foaming accelerator may contain lignin.

[0058] The molecular weight of PVA can range from 18,000 d to 130,000 d, and the basicity of PVA can be between 70% and 99%.

[0059] Based on the total weight of the second biodegradable material, the second biodegradable material may further contain 15 wt% to 35 wt% plasticizer.

[0060] Plasticizers may include at least one of small molecule polyols, polyethylene glycol, glycerides, and citrates.

[0061] Due to the high hydrophilicity of PVA, previous technologies have involved dissolving PVA in hot water before further processing. However, PVA aqueous solutions cannot be used for thermoplastic molding processes; moreover, the foamed structure obtained from this PVA aqueous solution process consists of open and interconnected pores, lacking sufficient mechanical support, making it prone to compression deformation and unsuitable for use in shoe soles.

[0062] Therefore, in one embodiment of the present invention, hot melt extrusion granulation can be used to first obtain thermoplastic PVA granules, and then PBAT granules and PVA granules are modified and extruded to obtain PBAT / PVA modified granules, and then foamed shoe soles are obtained by supercritical injection molding foaming method.

[0063] Thermoplastic PVA granules are produced by extruding PVA raw materials using a twin-screw extruder at a feed tube temperature between 180°C and 210°C.

[0064] PBAT / PVA modified granules are produced by mixing PBAT and PVA granules and then extruding them using a twin-screw extruder at a feed tube temperature of 170°C to 210°C.

[0065] In PBAT / PVA modified particles, the proportion of PBAT can be 70 to 95 wt%, and the proportion of PVA can be 5 to 30 wt%. The melt flow rate (MFR) of the resulting PBAT / PVA modified material is 1 to 5 gm / 200℃. [·]10min.

[0066] Therefore, the first biodegradable material and the second biodegradable material can each be in the form of independent colloidal particles, or both can be in the form of modified colloidal particles.

[0067] The present invention also provides a method for manufacturing biodegradable foamed shoe soles.

[0068] Figure 1 is a flowchart of a method for manufacturing a biodegradable foamed shoe sole according to the present invention.

[0069] Referring to FIG1, a method for manufacturing a biodegradable foamed shoe sole according to the present invention includes: a melting step S1, melting any of the above-mentioned materials for manufacturing a biodegradable foamed shoe sole; a mixing step S2, mixing the molten material with a supercritical gas to obtain a polymer melt containing the supercritical gas; an injection step S3, injecting the polymer melt into a mold; and a foaming molding step S4, depressurizing the mold and cooling the polymer melt therein to foam and shape the polymer melt, thereby manufacturing a biodegradable foamed shoe sole.

[0070] In this invention, the supercritical gas used as the foaming agent in injection molding foaming can be N2.

[0071] Specifically, the melting step S1, the mixing step S2, and the injection step S3 can be performed using foam injection molding equipment.

[0072] Figure 2 is an apparatus diagram of a foam injection molding equipment 1 for manufacturing biodegradable foamed shoe soles according to an embodiment of the present invention.

[0073] Referring to Figure 2, in the melting step S1, the material for manufacturing the biodegradable foamed sole is fed into the foaming injection molding equipment 1 via the hopper 11 and conveyed to the feed pipe 12. In the feed pipe 12, it is melted and stirred by a screw 13 and heating. In the mixing step S2, supercritical gas from the gas cylinder 16 is further injected into the feed pipe 12. In the feed pipe 12, the supercritical gas is stirred and mixed with the molten material for manufacturing the biodegradable foamed sole by the shearing force of the screw 13. In the injection step S3, the polymer melt is injected into the mold 15 through the injection nozzle 14 of the foaming injection molding equipment 1. Subsequently, the foaming molding step S4 is performed in the mold 15.

[0074] The present invention also provides a biodegradable foam sole manufactured by any of the above-described methods for manufacturing biodegradable foam soles.

[0075] Specifically, the biodegradable foamed sole has a foaming ratio of 7 to 9 times, a resilience of 45% to 70%, a compression set of 50% to 70%, and a shrinkage rate of 0.1% to 0.5%. [Experimental Methods]

[0076] The effectiveness of the solution proposed in this invention will be verified through specific embodiments below. [Example] [1] [Testing suitable biodegradable foam materials]

[0077] Using CO2 as a supercritical foaming agent gas, small-scale supercritical gas autoclaving was conducted on degradable materials PBAT, PBS, PVA, and cellulose acetate in granular form. The foaming feasibility test was carried out on several materials that can be degraded by home composting in order to preliminarily screen the degradable materials that are more suitable for supercritical gas foaming and the more suitable processing parameter range.

[0078] The heating temperature (mold temperature) for autoclaving is 115℃ to 150℃, the gas pressure is 17 to 25MPa, and the permeation time is 90 to 180 minutes, for example, 90 minutes.

[0079] Figure 3 shows the foaming effects of different biodegradable materials according to Example 1 of the present invention (in Figure 3, a represents PBS, b represents PBAT, c represents PVA, and d represents cellulose acetate). Among them, PBAT showed the best foaming effect compared to PBS, PVA, and cellulose acetate, and its foaming ratio and foam texture were most suitable for use in foamed shoe soles. Therefore, the present invention selected PBAT as the first biodegradable material for further development. [Example] [2] [Tests on supercritical gas autoclaving foaming and supercritical gas injection molding foaming]

[0080] Using N2 as a supercritical foaming agent gas, PBAT was subjected to supercritical gas autoclaving foaming and supercritical gas injection molding foaming to verify the industrialization feasibility of applying the newly developed supercritical gas injection molding foaming to the production of PBAT foamed shoe soles.

[0081] In the autoclaved aerated concrete (PAC) foaming method, PAC is first molded into sheets of appropriate size using an injection molding machine, and then placed in a supercritical autoclaved aerated concrete (SAC) foaming equipment for foaming. The heating temperature is 125℃ to 145℃, the gas pressure is 15 to 20 MPa, and the permeation time is 90 minutes.

[0082] In the injection molding foaming method, the temperature of the feed tube is 190℃ to 210℃, the pressure of the mixing tube section is 18 to 20MPa, the gas usage is 25% to 40%, the molding pressure is 2 to 3.5MPa, the injection speed is 90 to 115mm / s, and the specific gravity of the finished product is 0.14 to 0.22.

[0083] Table 1 and Figure 4 show a comparison of supercritical gas autoclaving foaming and supercritical gas injection molding foaming according to Example 2, and the foaming results, respectively.

[0084] [Table 1] Prior Technology Supercritical gas autoclave foaming This invention technology Supercritical gas injection molding foaming supercritical gas N2 N2 Processing methods First, the foamed sheets are manufactured by injection molding, and then supercritical gas foaming is performed using a pressure vessel mold. Direct injection molding, No need for secondary mold pressing

[0085] In Figure 4, a represents the foaming result of supercritical gas autoclaving, and b represents the foaming result of supercritical gas injection molding. The comparison between Table 1 and Figure 4 shows that, compared to previous technologies using supercritical gas autoclaving, this invention, using injection molding foaming, not only achieves the desired foaming effect (e.g., uniform bubble structure), but also further realizes the industrialization goal of continuous manufacturing and one-time foaming molding, successfully achieving the objectives of simplifying the process, reducing costs, increasing production efficiency, and thus improving industrialization efficiency.

[0086] In the following experimental methods, when injection molding foaming is mentioned, the same methods and conditions as those used for N2 supercritical gas injection molding foaming in Example 2 are employed.

[0087] In the experimental method of this invention, the performance analysis of foamed shoe soles is conducted using international standards commonly used in the industry (as shown in Table 2). All instruments and equipment used are calibrated and maintained, the testing environment meets the testing standards and specifications, and the operators are all qualified and skilled quality inspectors.

[0088] [Table 2] Test Project Test Standards hardness ASTM D2240 proportion ASTM D297 Rebound rate (%) ASTM D2632 Tensile strength (kg / cm2) ASTM D412 Elongation (%) ASTM D412 Tear strength (kg / cm) ASTM D624 Compression permanent deformation rate (%) ASTM D395 Shrinkage rate (%) BS5131 Delamination tear strength (kg / cm) 20min BS5131 [Example] [3] [:by] [CO, 2] [Supercritical gas for autoclaving and foaming of sheet materials] [N, 2] [Comparison of the performance of supercritical gas injection molding foam]

[0089] Furthermore, foamed shoe soles were manufactured by autoclaving with CO2 supercritical gas and by injection molding with N2 supercritical gas, and the differences between the two are shown in Table 3 below.

[0090] In the CO2 supercritical gas autoclaved plate foaming, except for the different foaming agent gas, the same method and conditions as those used in the N2 supercritical gas autoclaved plate foaming of Example 2 were employed.

[0091] [Table 3] Supercritical CO2 autoclaved sheet foaming Supercritical N2 injection molding foaming supercritical gas CO2 has a high cost. N2, lower cost Hardness (Shore C) 47 62 proportion 0.28 0.18 Foaming ratio 4.57 7.11 Rebound rate (%) 46 70 Compression permanent deformation rate (%) 72 67.8

[0092] The results in Table 3 show that, compared with the foamed shoe soles manufactured by autoclaving with supercritical CO2 gas in the prior art, the biodegradable foamed shoe sole of the present invention can not only produce PBAT foamed shoe soles in one process, but also has a lower specific gravity, the foaming ratio is increased from 4.57 times to 7.11 times (an increase of about 56%), the resilience rate is increased from 46% to 70% (an increase of about 52%), and the compression set is reduced from 72% to 67.8% (an improvement of about 6%). [Example] [4] [:] [PBAT] [Comparison of Injection Molding Foaming Performance with Different Additives]

[0093] To further understand the effects of adding lignin, PVA, and other components to PBAT foaming materials on the resulting foamed shoe soles, physical property tests were conducted on foamed shoe soles made from the following three samples H400, H4, and H50P05 through N2 supercritical gas injection molding of the present invention. The results are shown in Table 4 below.

[0094] Modified PBAT and PVA particles were prepared using the following method: [(] [1] Thermoplastic [PVA] [Gel Granule Manufacturing]

[0095] PVA is mixed evenly with optional plasticizers and lubricants and then fed into a conventional twin-screw extruder for extrusion granulation through a conventional process. The plasticizer can be a glycerol ester, and the lubricant can be a vegetable wax. [(] [2] [)] [PBAT / PVA] [Manufacturing of modified granules]

[0096] The obtained thermoplastic PVA granules are thoroughly mixed with PBAT and extruded and granulated using a twin-screw extruder through a conventional process.

[0097] [Table 4] Test Project Sample H400 (PBAT / Lignin) Sample H4 (PBAT / PVA) Sample H50P05 (PBAT / PVA / Lignin) hardness 63.8 63.5 59.6 proportion 0.19 0.18 0.2 Rebound rate (%) 53 50 47 Tensile strength (kg / cm2) 11.7 10.39 14.3 Elongation (%) 185.7 154.89 184.1 Tear strength (kg / cm) 15.8 15.44 15.6 Compression permanent deformation rate (%) 55 58.89 54.5 Shrinkage rate (%) 0.28 0.27 0.27 Delamination tear strength (kg / cm) 20min 4.54 4.63 4.63

[0098] In Table 4, sample H400 is a PBAT / lignin mixture with 4 wt% lignin added alone; sample H4 is a PBAT / PVA modified material with 5 wt% PVA added alone; and sample H50P05 is a PBAT / PVA / lignin modified material with 0.5 wt% lignin and 5 wt% PVA added.

[0099] The results in Table 4 show that, compared to the prior art (the foamed shoe sole manufactured by autoclaving with supercritical CO2 gas in Example 3, with a compression set of 72%), the compression set of the foams made from samples H400 (PBAT / lignin), H (PBAT / PVA), and H50P05 (PBAT / PVA / lignin) of the present invention was improved by approximately 24%, 18%, and 24%, respectively. These results also indicate that lignin and PVA can improve the compression set of PBAT foamed shoe soles, either individually or synergistically. [Example] [5] [In different] [PVA] [Comparison of Foaming Properties in Injection Molding under Different Degrees of Polymerization]

[0100] To further understand the effect of PVA polymerization degree on the foamed shoe soles, physical properties of foamed shoe soles made from PBAT and the following three PBAT / PVA modified samples H, MH and LH were tested without adding lignin and with the same foaming ratio. The results are shown in Table 5 below.

[0101] [Table 5] Test Project PBAT Sample H (High degree of polymerization) Sample MH (Medium aggregation degree) Sample LH (Low degree of polymerization) hardness 62.6 63.5 52.8 47.7 proportion 0.18 0.18 0.18 0.18 Rebound rate (%) 70 50 56 49 Tensile strength (kg / cm2) 14.5 10.39 11.2 11.3 Elongation (%) 225 154.89 147.7 157.7 Tear strength (kg / cm) 9.75 15.44 12.4 13.5 Compression permanent deformation rate (%) 67.8 58.89 53.85 54.65 Shrinkage rate (%) 0.41 0.27 0.14 0.17 Delamination tear strength (kg / cm) 20min 4.62 4.63 4.47 4.32

[0102] In Table 5, sample H is a PBAT / PVA modified material with 5 wt% high degree of polymerization PVA (molecular weight from 115,000 d to 1,300,000 d); sample MH is a PBAT / PVA modified material with 5 wt% medium degree of polymerization PVA (molecular weight from 75,000 d to 90,000 d); and sample LH is a PBAT / PVA modified material with 5 wt% low degree of polymerization PVA (molecular weight from 18,000 d to 28,000 d).

[0103] Among them, compared with pure PBAT foam, the compression set of foamed shoe soles made from PBAT / PVA modified samples H, MH, and LH was reduced by 13% to 21%.

[0104] Furthermore, referring to Tables 3 and 5, it can be seen that compared to the prior art (the foamed shoe sole manufactured by autoclaving with supercritical CO2 gas in Example 3 had a compression set of 72%), the compression set of the foamed shoe soles made from samples H, MH, and LH of the present invention is improved by approximately 18%, 25%, and 24%, respectively. Overall, the compression set is improved by 18% to 25%.

[0105] In addition, referring to Table 5, it is worth noting that for foamed soles made of samples H, MH and LH, the hardness decreases significantly as the degree of polymerization of PVA decreases, but the compression set does not change significantly. Therefore, the hardness of foamed soles can be adjusted by the degree of polymerization of PVA without affecting the compression set, thus making it applicable to a wider range of shoe types with a wider demand for sole hardness.

[0106] Furthermore, as shown in Table 5, the shrinkage rate of foamed shoe soles tends to decrease as the degree of polymerization of PVA decreases. Therefore, the shrinkage rate of foamed shoe soles can also be adjusted by the degree of polymerization of PVA. [Example] [6] Comparison of foaming performance in injection molding at different foaming ratios

[0107] To further understand the effect of the foaming ratio of PBAT / PVA modified materials on the foamed shoe soles made from them, physical property tests were conducted on foamed shoe soles made from PBAT and the following four PBAT / PVA modified samples HP05A to HP05D. The results are shown in Table 6 below.

[0108] The foaming ratio of PBAT and PBAT / PVA modified samples was controlled by injecting PBAT and samples HP05A to HP05D with different feed amounts into a mold of the same known volume for injection foaming. Under the same mold volume, the smaller the feed amount, the higher the foaming ratio.

[0109] [Table 6] Test Project PBAT Sample HP05A Sample HP05B Sample HP05C Sample HP05D hardness 62.6 52.6 53.1 55.2 63.5 proportion 0.18 0.15 0.16 0.17 0.19 Foaming ratio 7.11 8.53 8.0 7.11 6.74 Rebound rate (%) 70 46 49 50 50 Tensile strength (kg / cm2) 14.5 7.97 9.47 10.44 14.31 Elongation (%) 225 67.41 107.97 139.2 184.09 Tear strength (kg / cm) 9.75 8.76 10.92 12.36 15.44 Compression permanent deformation rate (%) 67.8 57.14 57.09 58.01 58.89 Shrinkage rate (%) 0.41 0.36 0.24 0.3 0.27 Delamination tear strength (kg / cm) 20min 4.62 3.65 4.04 4.32 4.63

[0110] In Table 5, samples HP05A to HP05D are all PBAT / PVA modified materials with 5 wt% PVA having a molecular weight of 11,500 d to 130,000 d.

[0111] Different weights of PBAT / PVA modified materials, from smallest to largest: sample HP05A, sample HP05B, sample HP05C, and sample HP05D, were placed into a mold of the same volume and allowed to foam and form foamed shoe soles, thus obtaining four types of foamed shoe soles with different foaming ratios.

[0112] The results in Table 6 show that, among samples HP05A to HP05D, the higher the foaming ratio, the lower the compression set, that is, the better the compression set.

[0113] Referring to Tables 3 and 6, it can be seen that compared with the prior art (the foamed shoe sole manufactured by supercritical CO2 gas pressing of sheet material in Example 3, with a foaming ratio of 4.57 times and a compression set of 72%), in this invention, through supercritical N2 injection molding foaming, the foaming ratio of the foamed shoe sole made of PBAT foam material is increased from 4.57 times to 7.11 times, and the foaming ratio of the foamed shoe sole made of PBAT / PVA modified foam material is further increased to 8.53 times, while the compression set is significantly improved (by about 21%).

[0114] In summary, as shown in Tables 3 to 6, the PBAT and PVA and / or lignin modified material foam produced by the supercritical N2 injection molding foaming method of the present invention has excellent properties such as low specific gravity (as low as 0.15), high resilience (as high as 70%), low compression set (as low as 53.85%), and low shrinkage (as low as 0.14). Compared with the pure PBAT foam produced by the supercritical CO2 autoclave foaming method in the prior art (such as Example 3, specific gravity of 0.28, compression set of 72%), the specific gravity is reduced by nearly 50%, and the compression set is reduced by nearly 30%. Furthermore, compared with the pure PBAT foam produced by the supercritical N2 injection molding foaming method (such as Examples 5 and 6, shrinkage of 0.41%), the shrinkage is reduced by more than 60% (65.9%).

[0115] 1: Foaming Injection Molding Equipment 11: Hopper 12: Material pipe 13: Screw 14: Injection nozzle 15: Mold 16: Gas cylinders S1: Melting step S2: Mixing Steps S3: Injection Steps S4: Foaming and Molding Steps

Claims

1. A material for manufacturing biodegradable foamed shoe soles, comprising: 70 wt% to 95 wt% of the first biodegradable material, which contains polybutylene terephthalate (PBAT). And 5 wt% of a second biodegradable material and / or 0.5 wt% to 4 wt% of a foaming accelerator, wherein the second biodegradable material comprises polyvinyl alcohol (PVA) and the foaming accelerator comprises lignin.

2. The material for manufacturing biodegradable foamed shoe soles as described in claim 1, comprising: The first biodegradable material comprises 70 wt% to 95 wt%; And 5 wt% to 30 wt% of the second biodegradable material and 0.5 wt% to 4 wt% of the foaming accelerator.

3. The material for manufacturing biodegradable foamed shoe soles as described in claim 1, wherein, The molecular weight of this polyvinyl alcohol is between 18,000 d and 130,000 d, and its alkalinity is between 70% and 99%.

4. The material for manufacturing biodegradable foamed shoe soles as described in claim 1, wherein, Based on the total weight of the second biodegradable material, the second biodegradable material further comprises 15 wt% to 35 wt% of a plasticizer, wherein the plasticizer includes at least one of small molecule polyols, polyethylene glycol, glycerides, and citrates.

5. The material for manufacturing biodegradable foamed shoe soles as described in claim 1, wherein, The first biodegradable material and the second biodegradable material are each in the form of independent colloidal particles, or the first biodegradable material and the second biodegradable material are in the form of modified colloidal particles.

6. A method for manufacturing a biodegradable foamed shoe sole, comprising: The process includes a melting step, in which the material for manufacturing a biodegradable foamed sole as described in any one of claims 1 to 5 is melted; a mixing step, in which the molten material is mixed uniformly with a supercritical gas to obtain a polymer melt containing the supercritical gas; an injection step, in which the polymer melt is injected into a mold; and a foaming molding step, in which the mold is depressurized and the polymer melt therein is cooled to foam and shape the polymer melt, thereby manufacturing a biodegradable foamed sole.

7. The method for manufacturing a biodegradable foamed shoe sole as described in claim 6, wherein, The supercritical gas is N2.

8. The method for manufacturing a biodegradable foamed shoe sole as described in claim 6, wherein, The melting step, the mixing step, and the injection step are performed using a foam injection molding equipment. In the melting step, the material for manufacturing biodegradable foam soles is fed into the feed tube of the foam injection molding equipment and melted and stirred in the feed tube by means of a screw and heating. In the mixing step, supercritical gas is further injected into the feed tube, and the supercritical gas is stirred and mixed with the molten material in the feed tube by the shear force of the screw. In the injection step, the polymer melt is injected into the mold through the injection nozzle of the foam injection molding equipment.

9. A biodegradable foamed sole, obtained by foaming a material used to manufacture biodegradable foamed soles, wherein, The material used to manufacture the biodegradable foamed sole comprises: 70 wt% to 95 wt% of a first biodegradable material comprising polybutylene adipate terephthalate (PBAT); and 5 wt% of a second biodegradable material and / or 0.5 wt% to 4 wt% of a foaming accelerator, wherein the second biodegradable material comprises polyvinyl alcohol (PVA) and the foaming accelerator comprises lignin.

10. The biodegradable foam sole as described in claim 9, wherein, The biodegradable foam sole has a foaming ratio of 7 to 9 times, a rebound rate of 45% to 70%, a compression set rate of 50% to 70%, and a shrinkage rate of 0.1% to 0.5%.

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